I upgraded my husband's X61s from Vista to W7 Ultimate last year -- he uses it at home and has to run VPN software for the Army on it -- mostly does email, but also is able to send and receive signed documents here at home. He also travels quite a bit, and the X61s travels with him instead of his army-assigned computer. Windows 7 works great for him -- he doesn't want to be bothered with anything -- just wants to turn the machine on and have it work -- he's very happy with W7.
I also have W7 on the X60s I sent to Afghanistan with my middle kid (he didn't want to 'risk' his T60 when he deployed, but he was perfectly happy to take mom's X60s with him -- I upgraded that X60s from XP Pro to W7 Professional -- the son mostly net surfs, youtube/amazon/itunes/facebook, etc. He's happy with the W7 setup.
Youngest son (with Down Syndrome) uses an X61 when we travel -- that machine is also upgraded from XP Pro to W7 Pro, and son mostly does youtube and email -- lots and lots and lots of youtube music --
So each of our X machines are used a little differently, but all run on Windows 7, and each one is running a 128gb SSD with either 3 or 4gb of ram, although each machine can only use 3gb because they are all 32 bit machines. I never have to do anything to the machines as far as upkeep -- they are easy keepers